1. Field of the Invention
The present invention relates to improvements in electric power distribution systems for automotive vehicles. It relates particularly to the provision of an electric power distribution system incorporating power switches over which power is made available throughout a vehicle, and to a control system for controlling the power switches and thus the distribution of power.
2. Description of the Prior Art
Automotive vehicles require power for many elements such as running lights, turn indicator lights, emergency lights, horns, electric window lifts, radios, dome lights, air conditioners, and others. Many of these elements require the use of separate circuits, each with its own switching means. As a result, the wire networks in modern automotive vehicles have become very complicated. These systems characteristically involve dozens of separate wiring circuits to enable control of power to the moving power consuming components.
This requirement for numerous circuits has been attended by requirements for increasing amounts of current for many of the circuits. It has led to the use in each vehicle of many wires and cables having high current carrying capacity to interconnect the power supply through relatively large switches to the respective power consuming elements.
These requirements for large and heavy duty switches and especially for wiring of high current carrying capacity have placed heavy burdens on both the manufacturing and servicing of automotive vehicles. The costs in terms of materials required, space available in the vehicles, time required to assemble wiring harnesses and time to install them in the vehicles are very high. Repairs in case of failure are time-consuming and costly. The process of installing individual power lines for each function is costly in that each vehicle must have a wiring harness tailored specifically to fit it, meaning that a number of different wiring harnesses must be manufactured for each model of vehicle, depending upon optional equipment in individual examples of the model, in order to avoid excessive waste of expensive wiring.
Proposed solutions to these problems include the use of a pair of bus bars which are coupled by serially related relays to each of the power-consuming devices. U.S. Pat. Nos. 3,649,841 and 3,723,751 show such systems. Such systems include a complex network of small wires to control the relays and reduce the amount of heavy wiring. Among the disadvantages of such systems are the complex signaling and switching apparatus necessary in addition to the dual bus bar arrangement.
Other systems have been proposed which employ coded or timing signals to operate electronic switches on a time-sharing basis and couple power from a common bus bar to each power-consuming device. Examples of such systems are shown in U.S. Pat. Nos. 3,564,280 and 3,648,057. These systems substitute electronic complexity for wiring complexity. In order to minimize the number of control wires required, the code signals are transmitted on a time-division multiplex (TDM) basis over a common signal wire. This means the electronic switches must include logic means for determining which signals are pertinent to control each switch. Problems involving adequate shielding for the control wires to prevent transient voltages from disrupting the signals, of providing suitable electronic generators for the TDM signals and of providing suitable electronic logic circuits and electronic switches to respond to the signals militate against the use of such systems.